The present invention relates to subterranean treatments and, more particularly, in certain embodiments, to methods and compositions that utilize solid particles having an expandable coating in subterranean treatments.
In subterranean operations, there may be instances where it can be desirable to limit or prevent the flow a fluid into or through a particular portion of the subterranean formation or well bore. For example, it may be desirable to limit or prevent the loss of circulation of fluids, such as drilling fluids, into the subterranean formation. Such fluids may be lost into fractures induced by excess fluid pressures, into pre-existing fractures, or into large openings with structural strength in the formation, among other locations. This problem may be referred to as “lost circulation,” and the sections of the formation into which the drilling fluid may be lost may be referred to as “lost-circulation zones.” The loss of drilling fluids into the formation is undesirable, inter alia, because of the expense associated with the drilling fluid lost into the formation, loss of time, additional casing strings and, in extreme conditions, well abandonment. In addition to drilling fluids, problems with lost circulation may also be encountered with other fluids, for example, spacer fluids, completion fluids (e.g., completion brines), fracturing fluids, and cement compositions that may be introduced into a well bore.
In other instances, it may be desirable to limit or prevent the flow of water, which may be undesirably produced in subterranean operations. For example, when hydrocarbons are produced from wells that penetrate hydrocarbon-producing formations, water often accompanies the hydrocarbons, particularly as the wells mature over time. The water can be the result of a water-producing zones communicating with the hydrocarbon-producing formations or zones by fractures, high-permeability streaks, and the like. Alternatively, the water can be caused by a variety of other occurrences which are well known in the art, including water coning, water cresting, bottom water, channeling at the well bore, etc. The production of water adds undesired expense and complexity to the production of the hydrocarbons.
A number of different techniques have been developed to limit or prevent fluid flow into or through a particular portion of the subterranean formation or well bore, which may be useful in the prevention lost circulation and/or control of the undesirable production of water. In some instances, chemical systems have been used to limit or prevent fluid flow. One type of chemical system that has been used is chemical gels that resist the flow of injected fluids or the natural aqueous drive fluid through high permeability channels and fractures. The general approach has been to inject a mixture of reagents, initially low in viscosity, into a zone of the formation that has high permeability. After a sufficient time to allow the mixture to be pumped into the subterranean formation or when exposed to the elevated temperature of the formation, the mixture of reagents then forms a gel to block fluid flow. In addition, chemical systems commonly referred to as “relative permeability modifiers” have also been used to decrease the production of water. One example of a commonly used relative permeability modifier is polyacrylamide. These methods typically work at the formation face and/or well bore; however, in some instances formation damage may occur.
In addition to chemical systems, additional techniques that have been used for lost circulation control involve the placement of lost-circulation materials into the lost circulation zone. Conventional lost-circulation materials may include fibrous, lamellated or granular materials. The lost-circulation materials may be placed into the formation, inter alia, as part of a drilling fluid or as a separate lost-circulation pill in an attempt to control and/or prevent lost circulation. The lost-circulation materials typically form a seal in the lost-circulation zone (e.g., by packing off perforation tunnels, plating off a formation surface, plating off a hole behind a slotted liner, or packing along the surface of a hydraulic fracture) that prevents loss circulation of the drilling or other fluid into the formation. However, it is often desired to subsequently remove the lost-circulation materials to allow the maximum flow of produced fluids that comprise hydrocarbons from the subterranean zone to flow into the well bore. Subsequent operations necessary for removing such lost-circulation materials often entail considerable time and expense and added complications.